Tennis great Serena Williams has hinted she's pregnant with her first child on Snapchat.

Nearly four months after announcing her engagement to Reddit co-founder Alexis Ohanian, Serena Williams has strongly hinted she is expecting.

Sharing a sneaky shot on Snapchat, the 35-year-old posted an image of herself in a bright yellow swimsuit with the caption “20 weeks”.

Arguably the greatest tennis player of all time, Serena's growing baby bump is clearly on display in the photograph.

Mysteriously, Serena deleted the snap from her account and has not made any further comment on her pregnancy.

If Williams is indeed 20 weeks along, it means she was approximately two months pregnant when she won her 23rd Grand Slam at the Australian Open in January this year.

Serena's announcement comes just three days after she posted a selfie from her bed telling her 5.5 million followers that she was "fighting to get up".

Fighting to get up this morning

A post shared by Serena Williams (@serenawilliams) on Apr 16, 2017 at 6:07am PDT

Now, her fans have commented that she sports star was clearly in the midst of a bad bout of morning sickness.

"That morning sickness AIN'T NO JOKE....feel better," wrote one fan.

Another commented, "Baby makes you soooo sleepy".

In December last year, Williams announced she was engaged to Ohanian via a poem posted on Reddit.

"I came home a little late," Williams wrote in a thread she called 'I Said Yes'.

My only regret is not pointing my toe sorry coach Garry ????

A post shared by Serena Williams (@serenawilliams) on Apr 17, 2017 at 6:29am PDT

"Someone had a bag packed for me and a carriage awaited...Down on one knee he said 4 words and I said yes."

Ohanian, 33, responded to the post, commenting that Serena had made him "the happiest man on the planet".

Congratulations are in order for the parents-to-be!

LISTEN: Serena Williams schools us in how not to apologise for your work.

What do you think of Serena's baby news?